Touch sensor pattern

ABSTRACT

A capacitive sensor array includes a second sensor element intersecting a first sensor element to form an intersection associated with a unit cell. The second sensor element includes, within the unit cell: a first primary trace crossing the unit cell and a second primary trace crossing the unit cell, a first secondary trace connecting the first primary trace and the second primary trace, and a first tertiary trace branching away from the first secondary trace between the first primary trace and the second primary trace. An area of the first sensor element is greater than an area of the second sensor element within the unit cell.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/424,361, filed Mar. 19, 2012, which claims priority to U.S.Provisional Application No. 61/602,534, filed Feb. 23, 2012, all ofwhich are incorporated by reference herein in their entirety.

TECHNICAL FIELD

This disclosure relates to the field of touch-sensors and, inparticular, to trace patterns of elements in capacitive touch-sensorarrays.

BACKGROUND

Computing devices, such as notebook computers, personal data assistants(PDAs), kiosks, and mobile handsets, have user interface devices, whichare also known as human interface devices (HID). One user interfacedevice that has become more common is a touch-sensor pad (also commonlyreferred to as a touchpad). A basic notebook computer touch-sensor pademulates the function of a personal computer (PC) mouse. A touch-sensorpad is typically embedded into a PC notebook for built-in portability. Atouch-sensor pad replicates mouse X/Y movement by using two defined axeswhich contain a collection of sensor elements that detect the positionof one or more conductive objects, such as a finger. Mouse right/leftbutton clicks can be replicated by two mechanical buttons, located inthe vicinity of the touchpad, or by tapping commands on the touch-sensorpad itself. The touch-sensor pad provides a user interface device forperforming such functions as positioning a pointer, or selecting an itemon a display. These touch-sensor pads may include multi-dimensionalsensor arrays for detecting movement in multiple axes. The sensor arraymay include a one-dimensional sensor array, detecting movement in oneaxis. The sensor array may also be two dimensional, detecting movementsin two axes.

Another user interface device that has become more common is a touchscreen. Touch screens, also known as touchscreens, touch windows, touchpanels, or touchscreen panels, are transparent display overlays whichare typically either pressure-sensitive (resistive or piezoelectric),electrically-sensitive (capacitive), acoustically-sensitive (surfaceacoustic wave (SAW)) or photo-sensitive (infra-red). The effect of suchoverlays allows a display to be used as an input device, removing thekeyboard and/or the mouse as the primary input device for interactingwith the display's content. Such displays can be attached to computersor, as terminals, to networks. Touch screens have become familiar inretail settings, on point-of-sale systems, on ATMs, on mobile handsets,on kiosks, on game consoles, and on PDAs where a stylus is sometimesused to manipulate the graphical user interface (GUI) and to enter data.A user can touch a touch screen or a touch-sensor pad to manipulatedata. For example, a user can apply a single touch, by using a finger totouch the surface of a touch screen, to select an item from a menu.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1 is a block diagram illustrating an embodiment of an electronicsystem that processes touch sensor data.

FIG. 2 is a block diagram illustrating an embodiment of an electronicsystem that processes touch sensor data.

FIG. 3A illustrates an embodiment of an electronic touch-sensing systemusing a dual solid diamond capacitive sensor pattern.

FIG. 3B illustrates an embodiment of a dual solid diamond capacitivesensor pattern.

FIG. 4A illustrates an embodiment of a capacitive sensor array having atrellis pattern.

FIG. 4B illustrates a unit cell of a capacitive sensor array, accordingto one embodiment.

FIG. 5A illustrates a unit cell of a capacitive sensor array, accordingto one embodiment.

FIG. 5B illustrates a unit cell of a capacitive sensor array, accordingto one embodiment.

FIG. 6A illustrates a unit cell of a capacitive sensor array, accordingto one embodiment.

FIG. 6B illustrates a unit cell of a capacitive sensor array, accordingto one embodiment.

DETAILED DESCRIPTION

The following description sets forth numerous specific details such asexamples of specific systems, components, methods, and so forth, inorder to provide a good understanding of several embodiments of thepresent invention. It will be apparent to one skilled in the art,however, that at least some embodiments of the present invention may bepracticed without these specific details. In other instances, well-knowncomponents or methods are not described in detail or are presented in asimple block diagram format in order to avoid unnecessarily obscuringthe present invention. Thus, the specific details set forth are merelyexemplary. Particular implementations may vary from these exemplarydetails and still be contemplated to be within the spirit and scope ofthe present invention.

An embodiment of a capacitive touch sensor pattern may be constructedfrom a single patterned layer of conductive material and may have atrace geometry that minimizes regional geometric disparity without theuse of excessive metal bridges.

In one embodiment, such a capacitive touch sensor pattern may includetwo sets of intersecting sensor elements, where each sensor element in afirst set intersects each sensor element of the other set. One set ofsensor elements may be used as transmit (TX) electrodes, while the otherset of sensor elements is used as receive (RX) electrodes in a mutualcapacitance sensing system. In an alternative embodiment, the sensorelements may be used in a self-capacitance sensing system. In oneembodiment, each of the sensor elements of one set includes a main traceand one or more primary subtraces branching from the main trace. Thesensor elements may also include one or more secondary subtracesbranching from the primary subtraces and one or more tertiary subtracesbranching away from the secondary subtraces.

In one embodiment, a touch sensor pattern may include a number of unitcells, where a unit cell corresponding to a TX-RX pair of sensorelements may be defined as an area wherein each point within the unitcell area is nearest to an intersection between the TX-RX pair than toany intersection between a different TX-RX pairing.

In one embodiment, each unit cell of a capacitive touch sensor patternmay contain a main trace crossing the unit cell, at least a portion of aprimary subtrace branching perpendicularly away from the main trace, atleast four secondary subtraces branching away from the primarysubtraces, and at least two tertiary subtraces branching away from eachof the secondary subtraces. In one embodiment, the main trace andsubtraces may form a grid-like pattern resembling a trellis.

In one embodiment, both TX and RX sets of sensor elements may beconstructed using a single patterned layer of conductive material, withbridges used to join sections of the sensor elements that are separatedat intersections between the TX and RX pairs.

FIG. 1 illustrates a block diagram of one embodiment of an electronicsystem 100 including a processing device 110 that may be configured tomeasure capacitances from a touch sensing surface 116 including acapacitive touch sensor pattern as described above. The electronicsystem 100 includes a touch-sensing surface 116 (e.g., a touchscreen, ora touch pad) coupled to the processing device 110 and a host 150. In oneembodiment, the touch-sensing surface 116 is a two-dimensional userinterface that uses a sensor array 121 to detect touches on the surface116.

In one embodiment, the sensor array 121 includes sensor elements121(1)-121(N) (where N is a positive integer) that are disposed as atwo-dimensional matrix (also referred to as an XY matrix). The sensorarray 121 is coupled to pins 113(1)-113(N) of the processing device 110via one or more analog buses 115 transporting multiple signals. In thisembodiment, each sensor element 121(1)-121(N) is represented as acapacitor.

In one embodiment, the capacitance sensor 101 may include a relaxationoscillator or other means to convert a capacitance into a measuredvalue. The capacitance sensor 101 may also include a counter or timer tomeasure the oscillator output. The processing device 110 may furtherinclude software components to convert the count value (e.g.,capacitance value) into a sensor element detection decision (alsoreferred to as switch detection decision) or relative magnitude. Itshould be noted that there are various known methods for measuringcapacitance, such as current versus voltage phase shift measurement,resistor-capacitor charge timing, capacitive bridge divider, chargetransfer, successive approximation, sigma-delta modulators,charge-accumulation circuits, field effect, mutual capacitance,frequency shift, or other capacitance measurement algorithms. It shouldbe noted however, instead of evaluating the raw counts relative to athreshold, the capacitance sensor 101 may be evaluating othermeasurements to determine the user interaction. For example, in thecapacitance sensor 101 having a sigma-delta modulator, the capacitancesensor 101 is evaluating the ratio of pulse widths of the output,instead of the raw counts being over or under a certain threshold.

In one embodiment, the processing device 110 further includes processinglogic 102. Operations of the processing logic 102 may be implemented infirmware; alternatively, it may be implemented in hardware or software.The processing logic 102 may receive signals from the capacitance sensor101, and determine the state of the sensor array 121, such as whether anobject (e.g., a finger) is detected on or in proximity to the sensorarray 121 (e.g., determining the presence of the object), where theobject is detected on the sensor array (e.g., determining the locationof the object), tracking the motion of the object, or other informationrelated to an object detected at the touch sensor.

In another embodiment, instead of performing the operations of theprocessing logic 102 in the processing device 110, the processing device110 may send the raw data or partially-processed data to the host 150.The host 150, as illustrated in FIG. 1, may include decision logic 151that performs some or all of the operations of the processing logic 102.Operations of the decision logic 151 may be implemented in firmware,hardware, software, or a combination thereof. The host 150 may include ahigh-level Application Programming Interface (API) in applications 152that perform routines on the received data, such as compensating forsensitivity differences, other compensation algorithms, baseline updateroutines, start-up and/or initialization routines, interpolationoperations, or scaling operations. The operations described with respectto the processing logic 102 may be implemented in the decision logic151, the applications 152, or in other hardware, software, and/orfirmware external to the processing device 110. In some otherembodiments, the processing device 110 is the host 150.

In another embodiment, the processing device 110 may also include anon-sensing actions block 103. This block 103 may be used to processand/or receive/transmit data to and from the host 150. For example,additional components may be implemented to operate with the processingdevice 110 along with the sensor array 121 (e.g., keyboard, keypad,mouse, trackball, LEDs, displays, or other peripheral devices).

The processing device 110 may reside on a common carrier substrate suchas, for example, an integrated circuit (IC) die substrate, or amulti-chip module substrate. Alternatively, the components of theprocessing device 110 may be one or more separate integrated circuitsand/or discrete components. In one embodiment, the processing device 110may be the Programmable System on a Chip (PSoC™) processing device,developed by Cypress Semiconductor Corporation, San Jose, Calif.Alternatively, the processing device 110 may be one or more otherprocessing devices known by those of ordinary skill in the art, such asa microprocessor or central processing unit, a controller,special-purpose processor, digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), or other programmable device. In an alternativeembodiment, for example, the processing device 110 may be a networkprocessor having multiple processors including a core unit and multiplemicro-engines. Additionally, the processing device 110 may include anycombination of general-purpose processing device(s) and special-purposeprocessing device(s).

In one embodiment, the electronic system 100 is implemented in a devicethat includes the touch-sensing surface 116 as the user interface, suchas handheld electronics, portable telephones, cellular telephones,notebook computers, personal computers, personal data assistants (PDAs),kiosks, keyboards, televisions, remote controls, monitors, handheldmulti-media devices, handheld video players, gaming devices, controlpanels of a household or industrial appliances, or other computerperipheral or input devices. Alternatively, the electronic system 100may be used in other types of devices. It should be noted that thecomponents of electronic system 100 may include all the componentsdescribed above. Alternatively, electronic system 100 may include onlysome of the components described above, or include additional componentsnot listed herein.

FIG. 2 is a block diagram illustrating one embodiment of a capacitivetouch sensor array 121 and a capacitance sensor 101 that convertschanges in measured capacitances to coordinates indicating the presenceand location of touch. The coordinates are calculated based on changesin measured capacitances relative to the capacitances of the same touchsensor array 121 in an un-touched state. In one embodiment, sensor array121 and capacitance sensor 101 are implemented in a system such aselectronic system 100. Sensor array 220 includes a matrix 225 of N×Melectrodes (N receive electrodes and M transmit electrodes), whichfurther includes transmit (TX) electrode 222 and receive (RX) electrode223. Each of the electrodes in matrix 225 is connected with capacitancesensing circuit 201 through demultiplexer 212 and multiplexer 213.

Capacitance sensor 101 includes multiplexer control 211, demultiplexer212 and multiplexer 213, clock generator 214, signal generator 215,demodulation circuit 216, and analog to digital converter (ADC) 217. ADC217 is further coupled with touch coordinate converter 218. Touchcoordinate converter 218 may be implemented in the processing logic 102.

The transmit and receive electrodes in the electrode matrix 225 may bearranged so that each of the transmit electrodes overlap and cross eachof the receive electrodes such as to form an array of intersections,while maintaining galvanic isolation from each other. Thus, eachtransmit electrode may be capacitively coupled with each of the receiveelectrodes. For example, transmit electrode 222 is capacitively coupledwith receive electrode 223 at the point where transmit electrode 222 andreceive electrode 223 overlap.

Clock generator 214 supplies a clock signal to signal generator 215,which produces a TX signal 224 to be supplied to the transmit electrodesof touch sensor 121. In one embodiment, the signal generator 215includes a set of switches that operate according to the clock signalfrom clock generator 214. The switches may generate a TX signal 224 byperiodically connecting the output of signal generator 215 to a firstvoltage and then to a second voltage, wherein said first and secondvoltages are different.

The output of signal generator 215 is connected with demultiplexer 212,which allows the TX signal 224 to be applied to any of the M transmitelectrodes of touch sensor 121. In one embodiment, multiplexer control211 controls demultiplexer 212 so that the TX signal 224 is applied toeach transmit electrode 222 in a controlled sequence. Demultiplexer 212may also be used to ground, float, or connect an alternate signal to theother transmit electrodes to which the TX signal 224 is not currentlybeing applied. In an alternate embodiment the TX signal 224 may bepresented in a true form to a subset of the transmit electrodes 222 andin complement form to a second subset of the transmit electrodes 222,wherein there is no overlap in members of the first and second subset oftransmit electrodes 222.

Because of the capacitive coupling between the transmit and receiveelectrodes, the TX signal 224 applied to each transmit electrode inducesa current within each of the receive electrodes. For instance, when theTX signal 224 is applied to transmit electrode 222 through demultiplexer212, the TX signal 224 induces an RX signal 227 on the receiveelectrodes in matrix 225. The RX signal 227 on each of the receiveelectrodes can then be measured in sequence by using multiplexer 213 toconnect each of the N receive electrodes to demodulation circuit 216 insequence.

The mutual capacitance associated with each intersection between a TXelectrode and an RX electrode can be sensed by selecting every availablecombination of TX electrode and an RX electrode using demultiplexer 212and multiplexer 213. To improve performance, multiplexer 213 may also besegmented to allow more than one of the receive electrodes in matrix 225to be routed to additional demodulation circuits 216. In an optimizedconfiguration, wherein there is a 1-to-1 correspondence of instances ofdemodulation circuit 216 with receive electrodes, multiplexer 213 maynot be present in the system.

When an object, such as a finger, approaches the electrode matrix 225,the object causes a change in the measured mutual capacitance betweenonly some of the electrodes. For example, if a finger is placed near theintersection of transmit electrode 222 and receive electrode 223, thepresence of the finger will decrease the charge coupled betweenelectrodes 222 and 223. Thus, the location of the finger on the touchpadcan be determined by identifying the one or more receive electrodeshaving a decrease in measured mutual capacitance in addition toidentifying the transmit electrode to which the TX signal 224 wasapplied at the time the decrease in capacitance was measured on the oneor more receive electrodes.

By determining the mutual capacitances associated with each intersectionof electrodes in the matrix 225, the presence and locations of one ormore conductive objects may be determined. The determination may besequential, in parallel, or may occur more frequently at commonly usedelectrodes.

In alternative embodiments, other methods for detecting the presence ofa finger or other conductive object may be used where the finger orconductive object causes an increase in measured capacitance at one ormore electrodes, which may be arranged in a grid or other pattern. Forexample, a finger placed near an electrode of a capacitive sensor mayintroduce an additional capacitance to ground that increases the totalcapacitance between the electrode and ground. The location of the fingercan be determined based on the locations of one or more electrodes atwhich a change in measured capacitance is detected.

The induced current signal 227 is integrated by demodulation circuit216. The rectified current output by demodulation circuit 216 can thenbe filtered and converted to a digital code by ADC 217.

A series of such digital codes measured from adjacent sensor orintersections may be converted to touch coordinates indicating aposition of an input on touch sensor array 121 by touch coordinateconverter 218. The touch coordinates may then be used to detect gesturesor perform other functions by the processing logic 102.

In one embodiment, the capacitance sensor 101 can be configured todetect multiple touches. One technique for the detection and locationresolution of multiple touches uses a two-axis implementation: one axisto support rows and another axis to support columns. Additional axes,such as a diagonal axis, implemented on the surface using additionallayers, can allow resolution of additional touches.

FIG. 3A illustrates an embodiment of a capacitive touch sensing system300 that includes a capacitive sensor array 320. Capacitive sensor array320 includes a plurality of row sensor elements 331-340 and a pluralityof column sensor elements 341-348. The row and column sensor elements331-348 are connected to a processing device 310, which may include thefunctionality of capacitance sensor 101, as illustrated in FIG. 2. Inone embodiment, the processing device 310 may perform TX-RX scans of thecapacitive sensor array 320 to measure a mutual capacitance valueassociated with each of the intersections between a row sensor elementand a column sensor element in the sensor array 320. The measuredcapacitances may be further processed to determine higher resolutionlocations of one or more contacts at the capacitive sensor array 320.

In one embodiment, the processing device 310 is connected to a host 150which may receive the measured capacitances or calculate high precisionlocations from the processing device 310.

The sensor array 320 illustrated in FIG. 3A includes sensor elementsarranged in a diamond pattern. Specifically, the sensor elements 331-348of sensor array 320 are arranged in a single solid diamond (SSD)pattern. FIG. 3B illustrates a capacitive sensor array 321 having analternate embodiment of the diamond pattern, which is the dual soliddiamond (DSD) pattern. Each of the sensor elements of capacitive sensorarray 321 includes two rows or columns of electrically connected diamondshaped traces. Relative to the SSD pattern, the DSD pattern has improvedsignal disparity characteristics due to an increase in the couplingbetween TX and RX sensor elements while maintaining the sameself-capacitance coupling possible between each sensor element and aconductive object near the sensor element. The DSD pattern may alsoprovide higher sensitivity for tracking smaller objects, such as thepoint of a stylus, as compared to patterns having larger features, suchas SSD. However, the DSD pattern also increases the number of bridges(such as bridge 323) used to create the pattern, which may result indecreased manufacturing yield. The increased number of bridges may alsobe visible if metal bridges are used. For example, sensor array 321includes four bridges within unit cell 322.

FIG. 4A illustrates an embodiment of a capacitive sensor array 400having a grid-like trellis or lattice pattern. In contrast with the SSDand DSD patterns, the sensor array 400 may have increased signal,decreased noise, and increased manufacturing yield. In one embodiment,the capacitive sensor array 400 may be used to implement a multi-touchsensing surface controlled by a capacitive touch-screen controller,which may be implemented by a processing device such as device 110, forexample.

In one embodiment, capacitive sensor array 400 may be constructed byprinting, etching, depositing, or otherwise placing conductive materialonto a substrate. For example, the sensor array pattern may beconstructed from Indium Tin Oxide (ITO) or some other conductivematerial deposited onto a transparent substrate such as glass to createa transparent touch-sensing surface.

As compared to the SSD and DSD patterns, an embodiment of the patternfor sensor array 400 may have a longer boundary length within each unitcell between the TX and RX sensor elements, while minimizing the numberof metal bridges per unit cell. This results in a pattern capable ofproducing an increased signal level, and having a more uniformlydistributed sensitivity across the touch-sensing surface. In oneembodiment, such a pattern may also reduce the signal disparity betweengrounded and ungrounded systems. High coupling from the RX signals backto the AC ground of the TX buses may also increase the pattern'sresistance to injected noise sources.

With reference to FIG. 4A, capacitive sensor array 400 includes two setsof sensor elements. In one embodiment, sensor elements 401 may be usedas transmit (TX) sensor elements and sensor elements 402 may be used asreceive (RX) sensor elements in a mutual capacitance sensing system.Capacitive sensor array 400 is constructed such that each of the RXsensor elements 402 intersects each of the TX sensor elements to form aunit cell (such as unit cell 410) associated with each of theintersections between unique pairs of TX and RX elements. In oneembodiment, each point within the boundaries of each unit cell isnearest to an intersection between the corresponding TX-RX pair ofsensor elements than to any other intersection of a different TX-RXpair.

In one embodiment, each of the RX sensor elements 402 includes a maintrace that crosses at least one of the plurality of unit cells. FIG. 4Billustrates one unit cell 410 of capacitive sensor array 400, accordingto an embodiment. Within the unit cell 410, the RX sensor elementincludes a main trace 450 that crosses the unit cell 410, with at leasta portion of one or more primary subtraces, such as primary subtrace451, branching away from the main trace 450. In one embodiment, theprimary subtrace may branch away from the main trace such that alongitudinal axis of the primary subtrace is perpendicular to alongitudinal axis of the main trace at the junction between the maintrace and the primary subtrace.

Within the area of the unit cell 410, the RX sensor element may includea secondary subtrace, such as subtrace 452, that branches away from aprimary subtrace, such as subtrace 451. In one embodiment, the unit cell410 may include four secondary subtraces, as illustrated in FIG. 4B. Forexample, the sensor element 402 may include four primary subtraces(including subtrace 451) branching away from the main trace 450, and mayfurther include a secondary subtrace branching away from each of theprimary subtraces. In one embodiment, the secondary subtraces may have alongitudinal axis that is perpendicular to a longitudinal axis of theprimary subtrace from which it branches.

In one embodiment, the sensor element 402 may also include one or moretertiary subtraces (such as tertiary subtrace 453) branching away fromeach secondary subtrace. As illustrated in FIG. 4B, two tertiarysubtraces may branch away from each secondary subtrace. In oneembodiment, a longitudinal axis of each tertiary subtrace may beperpendicular to a longitudinal axis of the secondary subtrace fromwhich it branches.

In one embodiment, the tertiary subtraces may be rectangular, and mayhave two corners which can be described as “ear” vertexes. An ear vertexof a given shape may be described as any vertex where a line connectingthe vertexes on either side of the ear vertex passes through theinterior of the shape. In contrast, a “mouth” vertex is a vertex wheresuch a line lies outside the shape.

In one embodiment, the sensor element 402 may also include additionalprimary subtraces (such as subtraces 454) branching away from the maintrace 450. In one embodiment, these primary subtraces 454 may be alignedalong an axis with tertiary subtraces. The primary subtraces such assubtraces 454 may be rectangular in shape, and may be similar in shapeto the tertiary subtraces. Each of the primary subtraces may also havetwo corners that are ear vertexes.

In one embodiment, a bridge 455 may be used to connect portions of asensor element, such as TX sensor element 401. Bridge 455 may be madefrom metal or some other conductive material and may be used toelectrically connect the portions of sensor element 401 that areotherwise separated by the main trace 450 of sensor element 402. In oneembodiment, the sensor elements 402 and 401 are deposited on orconstructed from a single layer of conductive material. In oneembodiment, each unit cell of the capacitive sensor array pattern 400includes no more than one bridge. In one embodiment, the size of thebridge 455 may be reduced by tapering the TX or RX sensor elements atthe intersection to decrease the distance crossed by the bridge 455.

In one embodiment, the TX sensor element may fill substantially all ofthe negative space left by the RX sensor element, leaving a gap betweenthe edges of the RX and TX sensor elements. The gap may be uniform, ormay vary over the boundary length between the RX and TX sensor elements.

In one embodiment, the trellis pattern as illustrated in FIGS. 4A and 4Bresults in a longer boundary length between the TX and RX sensorelements, as compared to a similarly-sized area of the SSD or DSDpatterns. In one embodiment, this results in a higher touch signalsensitivity, and a more homogeneous distribution of sensitivitythroughout the unit cell.

In one embodiment, the trellis pattern of capacitive sensor array 400also provides a stronger path to ground, increasing noise immunity. Thetrellis pattern may also decrease signal disparity effects, while usingonly one bridge per unit cell to connect the sensor elements.

The trellis pattern may also allow for additional coupling when aconductive object is between sensor elements. This has the effect ofreducing the difference between the maximum observed signal and theminimum observed signal.

In one embodiment, the smaller features of the primary, secondary, andtertiary subtraces may allow detection of a smaller conductive object,such as a stylus tip, at the touch-sensing surface.

FIG. 5A illustrates a unit cell 500 of a simplified variation of thetrellis pattern, according to one embodiment. Unit cell 500 isassociated with an intersection between RX sensor element 502 and TXsensor element 501. Portions of sensor element 501 on either side of amain trace 506 of sensor element 502 are connected by a bridge 503.

In one embodiment, the RX sensor element 502 may include a primarysubtrace 505 branching perpendicularly away from the main trace 506, anda secondary subtrace 504 branching perpendicularly away from the primarysubtrace 505. In alternative embodiments, primary and secondarysubtraces may be added to the sensor element 502 to maximize theboundary length between the RX and TX sensor elements 502 and 501.

In one embodiment, the sensitivity distribution of a capacitive sensorarray may be controlled by the distribution of vertexes within each unitcell. Since charge tends to accumulate at the corners of the sensorelement, an even distribution of such vertexes may result incorresponding even distribution of sensitivity across the unit cell.

With reference to FIG. 4B, the shape of sensor element 402 that iscontained within unit cell 410 includes 32 ear vertexes formed by thecorners of the primary and tertiary subtraces. FIG. 5B illustrates anembodiment of a unit cell 550 for a capacitive sensor array patternwhere the tertiary subtraces and smaller primary subtraces are in theshape of triangles. The portion of RX sensor element 552 that is withinthe unit cell 550 includes 20 ear vertexes, eight of which are formed bythe points of the tertiary subtraces, four by the points of primarysubtraces, and eight by the corners of the rectangular secondarysubtraces. Bridge 553 connects the separate portions of the TX sensorelement 551. Alternative embodiments of the sensor pattern may have morethan 20 ear vertexes (such as the pattern illustrated in FIG. 4B).

In an alternative embodiment, the triangular traces in FIG. 5B mayinstead be replaced by other shapes, such as rectangles, circles,diamonds, stars, n-gons, or other shapes.

FIG. 6A illustrates a unit cell 600 of a capacitive sensor patternincluding an RX sensor element 602 and a TX sensor element 601,according to an embodiment. Separate portions of the TX sensor element601 are electrically connected by a bridge 603.

The RX sensor element 602 includes a main trace 606. Primary subtrace605 branches perpendicularly from the main trace 606, and secondarysubtrace 604 branches perpendicularly from primary subtrace 605. In oneembodiment, the secondary subtrace 604 is substantially in the shape ofa diamond. The sensor pattern illustrated in FIG. 6A eliminates a numberof vertexes relative to the trellis pattern illustrated in FIG. 4B.

FIG. 6B illustrates a unit cell 610 of a capacitive sensor patternincluding an RX sensor element 612 and a TX sensor element 611,according to an embodiment. Separate portions of the TX sensor element611 are electrically connected by a bridge 613.

The RX sensor element 612 includes a main trace 616. Primary subtrace615 branches perpendicularly from the main trace 616, and secondarysubtrace 614 branches perpendicularly from primary subtrace 615.

In one embodiment, the pattern illustrated in FIG. 6B is similar to thepattern of FIG. 4B, but with a different ratio between the areas of theRX and TX sensor elements. Thus, the ratio of these areas may beadjusted to affect performance parameters, such as signal disparityperformance, susceptibility to charger noise, and LCD noise immunity. Inone embodiment, the TX sensor elements may make up 50% of the area ofthe conductive material, while the RX sensor elements may make up theremaining 50% of the area.

In one embodiment, trace widths between sections of the TX sensorelement may be increased to reduce the resistance of the TX sensorelement. For example, the size of the tertiary subtraces, such assubtrace 617, may be decreased to increase the widths of the thinnerconnecting portions of the TX sensor element 611.

Embodiments of the present invention, described herein, include variousoperations. These operations may be performed by hardware components,software, firmware, or a combination thereof. As used herein, the term“coupled to” may mean coupled directly or indirectly through one or moreintervening components. Any of the signals provided over various busesdescribed herein may be time multiplexed with other signals and providedover one or more common buses. Additionally, the interconnection betweencircuit components or blocks may be shown as buses or as single signallines. Each of the buses may alternatively be one or more single signallines and each of the single signal lines may alternatively be buses.

Certain embodiments may be implemented as a computer program productthat may include instructions stored on a computer-readable medium.These instructions may be used to program a general-purpose orspecial-purpose processor to perform the described operations. Acomputer-readable medium includes any mechanism for storing ortransmitting information in a form (e.g., software, processingapplication) readable by a machine (e.g., a computer). Thecomputer-readable storage medium may include, but is not limited to,magnetic storage medium (e.g., floppy diskette); optical storage medium(e.g., CD-ROM); magneto-optical storage medium; read-only memory (ROM);random-access memory (RAM); erasable programmable memory (e.g., EPROMand EEPROM); flash memory, or another type of medium suitable forstoring electronic instructions.

Additionally, some embodiments may be practiced in distributed computingenvironments where the computer-readable medium is stored on and/orexecuted by more than one computer system. In addition, the informationtransferred between computer systems may either be pulled or pushedacross the transmission medium connecting the computer systems.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

What is claimed is:
 1. A capacitive sensor array comprising: a firstsensor element; and a second sensor element intersecting the firstsensor element to form an intersection associated with a unit cell, thesecond sensor element comprising, within the unit cell, a first primarytrace crossing the unit cell and second primary trace crossing the unitcell, a first secondary trace connecting the first primary trace and thesecond primary trace, and a first tertiary trace branching away from thefirst secondary trace between the first primary trace and the secondprimary trace, wherein an area of the first sensor element is greaterthan an area of the second sensor element within the unit cell.
 2. Thecapacitive sensor array of claim 1, wherein the first sensor elementcomprises a transmit (TX) sensor element and the second sensor elementcomprises a receive (RX) sensor element.
 3. The capacitive sensor arrayof claim 1, wherein the second sensor element further comprises, withinthe unit cell, a second secondary trace connecting the first primarytrace and the second primary trace and a second tertiary trace branchingaway from the second secondary trace between the first primary trace andthe second primary trace.
 4. The capacitive sensor array of claim 3,wherein a longitudinal axis of each of the first and second secondarytraces is perpendicular to the first and second primary traces at ajunction between the secondary trace and the primary trace.
 5. Thecapacitive sensor array of claim 3, wherein the first tertiary trace isaligned along a same axis as the second tertiary trace.
 6. Thecapacitive sensor array of claim 3, wherein at least a portion of atleast one of the first primary trace, the second primary trace, thefirst secondary trace, the second secondary trace, the first tertiarytrace or the second tertiary trace falls within a second unit cell. 7.The capacitive sensor array of claim 1, wherein the unit cell furthercomprises a single bridge coupled to the first sensor element.
 8. Acapacitive touch-sensing system comprising: a capacitive sensor arraycomprising a plurality of intersections between a plurality of firstsensor elements and a second sensor element, wherein each of theplurality of intersections is associated with a unit cell, the secondsensor element comprising, within each unit cell, a first primary tracecrossing the unit cell and second primary trace crossing the unit cell,a first secondary trace connecting the first primary trace and thesecond primary trace, and a first tertiary trace branching away from thefirst secondary trace between the first primary trace and the secondprimary trace, wherein an area of the first sensor element is greaterthan an area of the second sensor element within the unit cell; and acapacitance sensor coupled to the capacitive sensor array, wherein thecapacitance sensor is configured to measure a mutual capacitance foreach of the plurality of intersections between the plurality of firstsensor elements and the second sensor element.
 9. The capacitivetouch-sensing system of claim 8, wherein the first sensor elementcomprises a transmit (TX) sensor element and the second sensor elementcomprises a receive (RX) sensor element.
 10. The capacitivetouch-sensing system of claim 8, wherein the second sensor elementfurther comprises, within the unit cell, a second secondary traceconnecting the first primary trace and the second primary trace and asecond tertiary trace branching away from the second secondary tracebetween the first primary trace and the second primary trace.
 11. Thecapacitive touch-sensing system of claim 10, wherein a longitudinal axisof each of the first and second secondary traces is perpendicular to thefirst and second primary traces at a junction between the secondarytrace and the primary trace.
 12. The capacitive touch-sensing system ofclaim 10, wherein the first tertiary trace is aligned along a same axisas the second tertiary trace.
 13. The capacitive touch-sensing system ofclaim 10, wherein at least a portion of at least one of the firstprimary trace, the second primary trace, the first secondary trace, thesecond secondary trace, the first tertiary trace or the second tertiarytrace falls within a second unit cell.
 14. The capacitive touch-sensingsystem of claim 8, wherein the unit cell further comprises a singlebridge coupled to the first sensor element.
 15. A capacitive sensorarray comprising: a first plurality of sensor elements; and a secondsensor element intersecting each of the first plurality of sensorelements to form a plurality of intersections, wherein each of theplurality of intersections is associated with a unit cell, wherein theunit cell designates a set of locations nearest a correspondingintersection, the second sensor element comprising, within the unitcell, a first primary trace crossing the unit cell and second primarytrace crossing the unit cell, a first secondary trace and a secondsecondary trace each connecting the first primary trace and the secondprimary trace, a first tertiary trace branching away from the firstsecondary trace between the first primary trace and the second primarytrace, and a second tertiary trace branching away from the secondsecondary trace between the first primary trace and the second primarytrace, wherein an area of one of the first plurality of sensor elementsis greater than an area of the second sensor element within the unitcell.
 16. The capacitive sensor array of claim 15, wherein the firstplurality of sensor elements comprises transmit (TX) sensor elements andthe second sensor element comprises a receive (RX) sensor element. 17.The capacitive sensor array of claim 15, wherein a longitudinal axis ofeach of the first and second secondary traces is perpendicular to thefirst and second primary traces at a junction between the secondarytrace and the primary trace.
 18. The capacitive sensor array of claim15, wherein the first tertiary trace is aligned along a same axis as thesecond tertiary trace.
 19. The capacitive sensor array of claim 15,wherein at least a portion of at least one of the first primary trace,the second primary trace, the first secondary trace, the secondsecondary trace, the first tertiary trace or the second tertiary tracefalls within a second unit cell.
 20. The capacitive sensor array ofclaim 15, wherein the unit cell further comprises a single bridgecoupled to the one of the first plurality of sensor elements.